Laser apparatus and production method of laser apparatus

ABSTRACT

Provided are a laser apparatus into which a large current can be injected and a production method which enables easy production of the apparatus. A laser apparatus includes a light-emitting region on a substrate, and a periodic refractive index structure containing an i-type material provided at a periphery of the light-emitting region. Another laser apparatus includes a light-emitting region between a first electrode and a second electrode on a substrate, wherein at least one of the first and the second electrodes includes a periodic refractive index structure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a laser apparatus and a productionmethod of a laser apparatus.

2. Description of the Related Art

In general, a semiconductor laser device includes a p-type electrode, ann-type electrode, a p-type optical waveguide, an n-type opticalwaveguide, and an active layer

Being provided near the active layer and made of materials differentfrom the material constituting the active layer, the electrodes andoptical waveguides act as a resonator for confining the light generatedin the active layer.

By the above configuration, stimulated (or induced) emission of laserlight is caused in the active layer, and the laser light is amplified inthe resonator and then guided outside the device by the opticalwaveguides.

Moreover, there is also a configuration using a Fabry-Perot resonator inwhich a cleavage plane is used as a resonator.

However, since the above-mentioned resonators cannot spatially controllight perfectly, further improvement is required in order to achievesuch a laser device that is desired for use in optical communication anda light source for an optical disk, operates at a lower current, and hasa higher output.

Therefore, recently, as an ideal laser device, attention has beenfocused on a photonic crystal which can control the propagation of anelectromagnetic wave, in particular a light.

The photonic crystal is a structural member in which the refractiveindex of a constituent substance is distributed periodically and is anartificial material which can achieve novel functions only by means ofstructural design.

As a most remarkable feature of the photonic crystal, it has been knownthat a region referred to as a photonic bandgap, where a specificelectromagnetic wave cannot propagate, is formed due to the differencein refractive index of the constituent material and the periodicity ofthe structure.

By introducing a suitable defect into a refractive index distribution ina photonic crystal, an energy level due to the defect (defect level) isformed in the photonic bandgap. This enables the photonic crystal tocontrol an electromagnetic wave with perfect freedom. Besides, the useof the photonic crystal enables the size of a device to be reduced.

The largest advantage of using a photonic crystal as a resonator of alaser device is that since perfect spatial control of a light, which hasbeen hitherto impossible, can be achieved, a laser light can be obtainedwhich has an extremely small threshold value (theoretically zero) andsmall temperature dependences of the output and the wavelength.

Moreover, the advantage is also in that since the radiation of light canbe controlled with respect to the entire space, high electro-opticalconversion efficiency can be obtained.

Although, one dimensional, two dimensional, and three dimensionalphotonic crystals are present, in order to achieve the above-mentionedeffect to a maximum extent, the three dimensional photonic crystal ismost suitable.

In other words, the three dimensional photonic crystal has a featurethat the distribution of refractive index of the constituent substancehas a three dimensional periodicity, and an electromagnetic waveexisting at a position of a defect hardly leaks outside and is thereforemost suitable for controlling the propagation of an electromagneticwave.

A representative example of the three dimensional photonic crystal is awoodpile structure (or rod-pile structure) disclosed in U.S. Pat. No.5,335,240.

The woodpile structure, as illustrated in FIG. 7 has a structure havinga stacked stripe layers in which a plurality of rods are periodicallydisposed parallel to each other at a predetermined in-plane periodicity.

Specifically, the woodpile structure is configured such that each rodbelonging to each stripe layer intersects perpendicularly to each rodbelonging to a nearest neighbor stripe layer, and each rod belonging toeach stripe layer is parallel to each other and is offset by a half ofthe in-plane periodicity with each rod belonging to stripe layers beingapart therefrom by two layers.

The periodicity of the photonic crystal structure is an order of a halfof the wavelength of an electromagnetic wave to be controlled. Forexample, the periodicity of a photonic crystal for visible light isabout 250 nm.

In the prior art, as a semiconductor laser device using such a threedimensional photonic crystal, for example, in Japanese PatentApplication Laid-Open No. 2001-247425, a semiconductor laser devicehaving low threshold current characteristics, in which an active portionis provided in a three dimensional photonic crystal structure, and aproduction method thereof has been proposed. The proposed semiconductorlaser device has a structure such as illustrated in FIG. 8, in which anundoped InGaAs etch stop layer 1102 is formed on the surface of a highresistance InP substrate 1101.

Moreover, on the surface of the etch stop layer 1102, a threedimensional photonic crystal structure containing an active layer 1304is formed.

Furthermore, on the surface of the three dimensional photonic crystalstructure, a p-type electrode 1105 and an n-type electrode 1106 areformed via an InGaAs contact layer.

In other words, here, on the photonic crystal structure, there areformed electrodes composed of thin films of materials different from thematerial of the photonic crystal structure.

SUMMARY OF THE INVENTION

However, the prior art semiconductor laser device, disclosed in JapanesePatent Application Laid-Open No. 2001-247425, has the followingproblems.

The prior art semiconductor laser device has a problem such that sincethere are formed, on the photonic crystal structure, electrodes composedof thin films of materials different from the material of the photoniccrystal structure, it is difficult to inject a large amount of currentinto the active portion.

In other words, since the material provided between the electrode andthe pin junction is non-metallic material and different from theelectrode material, the series resistance between the electrode and thepin junction is large.

Therefore, there is a problem that the amount of current that can beinjected into the active portion is small.

Moreover, since the electrode is not transparent, there is posed aproblem that when light is emitted, the electrode may cast a shadowthereof, depending on the design.

Furthermore, since a plurality of different materials are required to bestacked, the production steps become complicated.

In view of the above-mentioned problems, the present invention providesa laser apparatus into which a large amount of current can be injected.

Moreover, the present invention provides a production method of a laserapparatus which enables easy production of the apparatus.

The present invention, in order to solve the above-mentioned problems,provides a laser apparatus with the following configuration, and aproduction method of the laser apparatus.

The laser apparatus according to the present invention includes alight-emitting region on a substrate, and a periodic refractive indexstructure including an i-type material provided at a periphery of thelight-emitting region.

Moreover, according to the present invention, the i-type material isi-type titanium oxide.

Moreover, according to the present invention, the periodic refractiveindex structure is formed of a three dimensional photonic crystal.

Moreover, according to the present invention, a layer comprising thelight-emitting region and the periodic refractive index structure has anelectrode of a three dimensional photonic crystal comprised of a p-typetitanium oxide material on one side of an upper side and a lower side ofthe layer, and an electrode of a three dimensional photonic crystalcomprised of an n-type titanium oxide material on the other side of thelayer.

Moreover, the laser apparatus according to the present inventionincludes a light-emitting region between a first electrode and a secondelectrode on a substrate, wherein, at least one of the first and thesecond electrodes includes a periodic refractive index structure.

Moreover, according to the present invention, both the first and thesecond electrodes include a periodic refractive index structure.

Moreover, according to the present invention, one of the first and thesecond electrodes which is located on the side from which laser light isoutput by the laser has a transparency with respect to the output laserlight.

Moreover, according to the present invention, a region which surroundsthe light-emitting region between the first and the second electrodes isformed of an i-type three dimensional photonic crystal.

Moreover, the method of producing a laser apparatus according to thepresent invention, includes: forming a first layer comprising a threedimensional periodic refractive index structure; forming a second layerwith a periodic structure region on the first layer; forming a recess inthe second layer and forming an active portion for generating light inthe recess; and forming a third layer comprising a three dimensionalperiodic refractive index structure on the second layer containing theactive portion.

Moreover, according to the present invention, the second layer is formedof an i-type material.

Moreover, according to the present invention, the production methodfurther includes providing a waveguide for extracting light outside, inthe three dimensional periodic refractive index structure of at leastone of the first and the third layers.

Moreover, according to the present invention, the three dimensionalperiodic refractive index structure of at least one of the first and thethird layers is formed of a material which is transparent with respectto visible light

Moreover, according to the present invention, the material which istransparent with respect to visible light comprises any one of titaniumoxide (TiO₂), gallium nitride (GaN), zinc oxide (ZnO), and indium tinoxide (ITO) as a main component.

Moreover, according to the present invention, the active portionincludes a material which generates visible laser light.

Furthermore, the present invention directed to a production method of alaser apparatus encompasses the following inventions.

The present invention is a method of producing a laser apparatus, whichincludes: forming a three dimensional photonic crystal structureincluding a material which is transparent with respect to visible light;forming a defect portion for housing an active portion for generatinglight; forming the active portion in the defect portion; and forming awaveguide for guiding laser light outside the photonic crystal.

Moreover, according to the present invention, the three dimensionalphotonic crystal structure is a woodpile structure whose periodicity is150 nm to 500 nm.

Moreover, according to the present invention, the active portion iscomprised of a material which generates visible laser light, and is aquantum dot of GaN or TiO₂, or a heterostructure of TiO₂/InGaN/TiO₂ orGaN/TiO₂/GaN.

Moreover, the present invention includes: the stacking step of forming athree dimensional photonic crystal structure; the first sub-step offorming an alignment mark comprised of a metal on a transparentsubstrate; the second sub-step of forming a first layer of a transparentmaterial thin film on the substrate; the third sub-step of forming afirst mask pattern using the alignment mark as a positional reference onthe transparent material thin film; the fourth sub-step of forming afirst layer structure of a three dimensional photonic crystal structureby processing the transparent material thin film from above the firstmask pattern; the fifth sub-step including the step of forming asacrifice layer thin film on a thin film containing the first layerstructure and the step of flattening the sacrifice layer thin film untilthe first layer structure is exposed; the step of forming a second andsubsequent layer structures of the transparent material constituting apredetermined three dimensional photonic crystal by repeating the secondto the fifth sub-steps a predetermined number of times using thealignment mark as a positional reference; and the step of removing thesacrifice layers together.

Moreover, according to the present invention, the step of forming adefect portion for housing the active portion in the photonic crystal isincluded in the production step of the photonic crystal structure, and,in the production step, the defect is formed by processing a transparentmaterial thin film structure at a predetermined position into apredetermined shape.

Moreover, according to the present invention, the step of forming awaveguide for guiding the laser light outside the photonic crystal isincluded in the production step of the photonic crystal structure, and,in the production step, the waveguide is formed by processing atransparent material thin film structure at a predetermined positioninto a predetermined shape.

Moreover, according to the present invention, the step of forming theactive portion in the defect portion is performed by a method includingchemical vapor deposition induced by a charged beam such as an electronbeam and a focused ion beam, after forming the defect portion forhousing the active portion.

Moreover, according to the present invention, the sub-step of formingthe transparent material thin film is a step of forming a titanium oxidethin film by means of sputtering, in which by forming an insulatingtitanium oxide thin film by use of a high-purity titanium oxide target,and by adding a predetermined element to the high-purity titanium oxidetarget, the conductivity type or conductivity of the titanium oxide thinfilm is controlled.

Moreover, according to the present invention, the sub-step of forming amask pattern on the transparent material thin film includes the step ofapplying a resist on the transparent material thin film and forming apredetermined resist pattern by means of photolithography or electronbeam exposure process, or the step of previously forming a thin filmsuch as of a metal on the transparent material thin film, then applyinga resist on the formed thin film, forming a predetermined resist patternby means of photolithography or electron beam exposure process, and thentransferring the resist pattern onto the thin film such as of the metalby means of ion milling or reactive ion etching.

Moreover, according to the present invention, the sub-step of processingthe transparent material thin film to form each layer structure of athree dimensional photonic crystal structure includes the step oftransferring the mask pattern onto the transparent material thin film bymeans of reactive ion etching, and the step of removing the maskpattern.

Moreover, according to the present invention, the sub-step of formingthe sacrifice layer thin film is the step of forming a thin film of amaterial that is easily flattened with respect to the transparentmaterial thin film in the subsequent flattening step, in particularcopper; and the sub-step of flattening the sacrifice layer thin filmsis, for example, the step of flattening a copper thin film by means ofchemical mechanical polishing.

Moreover, according to the present invention, the sub-step of removingthe sacrifice layer thin films together is a chemical etching step usingan appropriate liquid etchant or gaseous etchant.

Moreover, according to the present invention, a plurality of thealignment marks are provided corresponding to the number of stacklayers.

According to the present invention, a laser apparatus can be achievedwhich enables injection of a large current and easy production.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating theconfiguration of a laser apparatus according to first Embodiment of thepresent invention.

FIG. 2 is a schematic plane view illustrating a configuration example ofthe laser apparatus using an i-type three dimensional photonic crystalaccording to first Embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view illustrating theconfiguration of a laser apparatus according to second Embodiment of thepresent invention.

FIG. 4 is a schematic plane view illustrating a configuration example ofthe laser apparatus using an i-type three dimensional photonic crystalaccording to first Embodiment of the present invention.

FIGS. 5A, 5B, 5C, 5D, 5E, 5F, 5G, 5H and 5I are schematiccross-sectional views illustrating a production method of a laserapparatus according to third Embodiment and Example 1 of the presentinvention.

FIGS. 6A, 6B, 6C and 6D are schematic cross-sectional views illustratinga formation method of an active portion in Example 1 of the presentinvention.

FIG. 7 is a perspective view illustrating a conventional threedimensional photonic crystal with a woodpile structure disclosed in U.S.Pat. No. 5,335,240.

FIG. 8 is a cross-sectional view illustrating a conventionalsemiconductor laser device disclosed in Japanese Patent ApplicationLaid-Open No. 2001-247425.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments according to the present invention will bedescribed.

First Embodiment

First, a laser apparatus according to first Embodiment of the presentinvention will be described.

FIG. 1 is a schematic cross-sectional view illustrating a configurationof a laser apparatus according to this embodiment.

In FIG. 1, a laser apparatus 10, a substrate 11, an n-type threedimensional photonic crystal 12, an i-type three dimensional photoniccrystal 13, a p-type three dimensional photonic crystal 14, and anactive portion 15, are illustrated.

The laser apparatus 10 according to this embodiment is composed of then-type three dimensional photonic crystal 12, the i-type threedimensional photonic crystal 13, and the p-type three dimensionalphotonic crystal 14 provided on the substrate 11, and the active portion15 inserted into the i-type three dimensional photonic crystal 13, and awaveguide (not shown).

For example, the substrate 11 is formed of synthesized quartz, and then-type, i-type, and p-type three dimensional photonic crystals areformed of a three dimensional crystal composed of titanium oxide.

Moreover, the active portion 15 inserted into the i-type threedimensional photonic crystal 13 exhibits light emission action upon theinjection of an electric current.

The three dimensional photonic crystals 12, 13 and 14 each have, forexample, a woodpile structure whose periodicity is about 250 nm.

The numbers of stacking of the n-type and p-type three dimensionalphotonic crystals 12 and 14 are, for example, 12 layers, respectively,and the number of stacking of the i-type three dimensional photoniccrystal 13 is, for example, 2 layers.

In this embodiment, the n-type and p-type three dimensional photoniccrystals 12 and 14 are respectively used not only for an opticalconfinement effect, but also as electrodes for injecting current intothe active portion 15.

An electric current is supplied through the electrodes of the n-type andp-type three dimensional photonic crystals 12 and 14 to generate lightin the active portion 15, and the light localized in the active portion15 causes stimulated emission to amplify the light.

In addition, by guiding the light outside using the waveguide, a visiblelight laser device can be achieved.

The active portion 15 is composed of an n-type/i-type/p-type stackstructure, and as for the material thereof, for example, AlGaN/GaN/AlGaNand TiO₂/InGaN/TiO₂ can be used.

FIG. 2 is a schematic plane view illustrating a configuration example ofa laser apparatus using the i-type three dimensional photonic crystal20.

The photonic crystal 20 is composed of a rod-structure 21 comprised ofi-type titanium oxide, an active portion 22, and a waveguide 23.

The active portion 22 is provided at an intersection of the rodstructures at the center of the photonic crystal 20.

Moreover, the waveguides 23 has a structure, for example, one obtainedby removing one rod from the rod structure of the photonic crystal 20,and have a function of extracting light therethrough.

Although in this embodiment, the waveguide 23 is disposed in a directionparallel to the substrate plane, the waveguide 23 may be disposed in adirection perpendicular to the substrate plane.

According to the laser apparatus 10 of this embodiment, since the threedimensional photonic crystals 12 and 14 are utilized as also an n-typeand a p-type electrodes, respectively to reduce the series resistance, alarge current can be injected into the active portion 15.

Moreover, when the configuration of this embodiment is applied to asurface emitting device, since the electrodes are transparent and do notcast a shadow thereof during the light emission, the degree of freedomof device design can be increased.

Incidentally, the photonic crystal of the invention according to thisembodiment is not necessarily required to be a three dimensionalphotonic crystal, and, for example, a two dimensional photonic crystal(with a periodicity with regard to refractive index in a planedirection) may be used.

The same also applies to the following embodiments.

Second Embodiment

Next, a laser apparatus according to second Embodiment of the presentinvention will be described.

FIG. 3 is a schematic cross-sectional view illustrating theconfiguration of the laser apparatus of this embodiment.

In FIG. 3, a laser apparatus 30, a substrate 31, an i-type threedimensional photonic crystal 32, and an active portion 33, areillustrated.

The laser apparatus according to this embodiment is constituted byforming the three dimensional photonic crystal 32 of i-type titaniumoxide on the substrate made of, for example synthesized quartz, andinserting the active portion 33 in the center of the three dimensionalphotonic crystal 32 which exhibits a light emission action uponirradiation with light.

The i-type three dimensional photonic crystal 32 has, for example, awoodpile structure whose periodicity is about 250 nm, and the number ofstack layers is, for example, 24.

An external exciting light is injected into the active portion 33 togenerate light in the active portion 33, and the light localized in theactive portion 33 causes stimulated emission to amplify the light,whereby a visible light photonic crystal laser is achieved.

In FIG. 3, the active portion 33 is constituted of a quantum dot, andthe material thereof is, for example, GaN.

FIG. 4 is a schematic plane view illustrating a configuration example ofa laser apparatus using the i-type three dimensional photonic crystal 4.

The photonic crystal 40 is composed of a rod-structure 41 comprised ofi-type titanium oxide, an active portion 42, and a waveguide 43.

The active portion 42 is provided at an intersection of the rodstructures at the center of the photonic crystal 40.

Moreover, the waveguides 43 has a structure, for example, one obtainedby removing one rod from the rod structure of the photonic crystal 40,and have a function of extracting light therethrough.

Although in this embodiment, the waveguide 43 is disposed in a directionparallel to the substrate plane, the waveguide 43 may be disposed in adirection perpendicular to the substrate plane.

Third Embodiment

Next, a production method of a laser apparatus according to thirdEmbodiment of the present invention will be described. FIGS. 5A, 5B, 5C,5D, 5E, 5F, 5G, 5H and 5I are schematic cross-sectional viewsillustrating the production method of the laser apparatus according tothis embodiment.

Incidentally, like elements in the figure are denoted by like referencenumerals. However, the material, structure, shape, and numeral valuesaccording to the present invention, are not limited to those hereindescribed.

In FIGS. 5A, 5B, 5C, 5D, 5E, 5F, 5G, 5H and 5I, there are shown asubstrate 51, an alignment mark 52, an active portion 60, a resistpattern 54, a secondary mask pattern 55, a sacrifice layer 56, a defectportion 57 of a photonic crystal, and a transparent material thin film53.

In addition, a first portion of the three dimensional photonic crystal70, a second portion of the three dimensional photonic crystal 80, and athird portion of the three dimensional photonic crystal 90, arerespectively illustrated. Incidentally, for convenience of description,the structure of the three dimensional photonic crystal is supposed tobe a woodpile structure.

As illustrated in FIGS. 5A, 5B, 5C, 5D, 5E, 5F, 5G, 5H and 5I, theproduction method of a laser apparatus according to this embodiment,includes:

(1) the step of forming a three dimensional photonic crystal structurecomposed of a material which is transparent with respect to visiblelight;(2) the step of forming a defect portion for housing an active portionfor generating light;(3) the step of forming the active portion in the defect portion; and(4) the step of forming a waveguide for guiding laser light outside thephotonic crystal.

Next, the above-mentioned production method will be described in detailfurther.

First, the step shown in FIG. 5A is a first sub-step of forming analignment mark 52 comprised of a metal, on a transparent substrate 51.

The material of the substrate 51 is, for example, quartz or sapphire.The alignment mark 52 is a thin film pattern formed of, for example,chromium (Cr) in a thickness of 100 nm and gold (Au) in a thickness of500 nm, viewed from the substrate side.

In the formation of the pattern, for example, an ordinary lift-offprocess for a metal pattern is used. The number of the alignment marks52 is set in advance depending on the number of times of the alignmentrequired in the subsequent steps.

For example, when 12 layers are stacked, since the number of times ofaligning will be 12, the number of the alignment marks 52 is set to 12or more.

Next, the step shown in FIG. 5B is a second sub-step of forming a firsttransparent material thin film 53 on the substrate 51.

The material of the thin film is, for example, a material composed of,for example, titanium oxide (TiO₂), gallium nitride (GaN), zinc oxide(ZnO) or indium tin oxide (ITO) as a main component.

The method of deposition is, for example, a sputtering process. When thetransparent material thin film 53 is deposited, the alignment mark 52 isprotected in advance so that the transparent material thin film 53 isnot deposited on the alignment mark 52.

As the method of protection, for example, by covering a metal mask onthe alignment mark 52, the transparent material thin film 53 isdeposited only on a part on which a film is to be formed. The thicknessof the transparent material thin film 53 is 50 nm to 100 nm.

Next, the step shown in FIG. 5C is a third sub-step of forming a firstmask pattern on the transparent material thin film 53 using thealignment mark 52 as a positional reference.

In the method for forming the mask pattern, for example, by applying aresist on the transparent material thin film 53, and forming apredetermined resist pattern 54 by means of a photolithography orelectron beam exposure process, a mask pattern is formed.

Moreover, as needed, by previously forming a thin film such as of ametal on the transparent material thin film 53, and subsequently byapplying the resist on the transparent material thin film 53, apredetermined resist pattern 54 is formed by means of a photolithographyor electron beam exposure process.

After that, the resist pattern is transferred onto the thin film such asof the metal by using ion milling or reactive ion etching to form asecondary mask pattern 55.

The configuration of the metal thin film is a single layer film of, forexample, chromium (Cr), platinum (Pt), or gold (Au), or a multilayerfilm of these metals. The thickness of the metal thin film is, forexample, 10 nm to 500 nm.

The resist pattern 54 has such a shape that one layer of the woodpilethree dimensional photonic crystal can be formed therein.

The period of the photonic crystal is 150 nm to 500 nm, the rod width ofthe woodpile is 50 nm to 250 nm, and the rod length of the woodpile is10 μm to 500 μm. Moreover, the number of periods in the photonic crystalin a plane is 10 to 1000.

Next, the step illustrated in FIG. 5D, is a fourth sub-step ofprocessing the transparent material thin film 53 from above the firstmask pattern to form a first layer structure 71 of the three dimensionalphotonic crystal structure.

As a method of processing the transparent material thin film 53, first,by using the resist pattern 54 as a mask or by using both of the resistpattern 54 and the secondary mask pattern 55 as masks, the transparentmaterial thin film 53 is processed by means of, for example, reactiveion etching.

Then, the mask patterns are removed.

In order to remove the mask patterns, there can be employed a techniqueof removing the resist using, for example, oxygen plasma, and dissolvingthe metal thin film by means of wet etching.

Moreover, the step shown in FIG. 5E is a fifth sub-step including thestep of forming a sacrifice layer thin film 56 on a thin film containingthe first layer structure 71 and the step of flattening the sacrificelayer thin film 56 until the first layer structure 71 is exposed.

The sub-step of forming the sacrifice layer thin film 56 is a step offorming a thin film of a material that is easily flattened with respectto the transparent material thin film 53, in the subsequent flatteningstep, preferably a copper thin film.

Moreover, the sub-step of flattening the sacrifice layer thin film 56 isa step of flattening, for example, the copper thin film by means ofchemical mechanical polishing.

Next, the step shown in FIG. 5F is a step of forming the second andsubsequent transparent material layers constituting the threedimensional photonic crystal.

Here, using the alignment mark 52 as a positional reference, byrepeating the sub-steps 2 to 5 a predetermined number of times, a firstportion 70 and a second portion 80 of the predetermined threedimensional photonic crystal are formed.

The predetermined number of times is, for example, 4 to 12 times. Here,in the second portion 80 of the three dimensional photonic crystal, adefect portion 57 for housing an active portion for light generating isprovided.

The formation of the defect portion 57 can be achieved in a simplemanner in the step of producing the photonic crystal structure byappropriately designing the shape of the structure.

Similarly, as needed, a predetermined optical waveguide is formed in apredetermined part of the first and the second portions 70 and 80.

As for the method of forming the optical waveguide, for example, therecan be used a method in which a rod of the photonic crystal being incontact with the defect portion 57 is removed.

Moreover, as the main materials of the first and the second portions 70and 80 of the three dimensional photonic crystal, a same material isused. However, as needed, in order to adjust the conductivecharacteristics, a predetermined impurity is added to a predeterminedlayer.

For example, when the material of the photonic crystal is titaniumoxide, a film of titanium oxide is formed by means of sputtering, and Nbor Ta is homogeneously incorporated into a sputter target in advance

Next, the step shown in FIG. 5G, is a sub-step of forming the activeportion 60 in the defect portion 57.

The formation of the active portion 60 is performed after the defectportion 57 has been formed, and by means of, for example, chemical vapordeposition induced by a charged beam such as an electron beam or afocused ion beam

The active portion 60 is composed of a material which generates visiblelaser light, and is, for example, a quantum dot of GaN or TiO₂, or aheterostructure of TiO₂/InGaN/TiO₂ or GaN/TiO₂/GaN.

Next, the step shown in FIG. 5H is a sub-step of forming a third portion90 of the three dimensional photonic crystal.

Here, after being subjected to the fifth sub-step, by using thealignment mark 52 as a positional reference, the sub-steps 2 to 5 arerepeated at a predetermined number of times. The predetermined number oftimes is, for example, 4 to 12 times.

As needed, a predetermined optical waveguide is formed into apredetermined part of the third portion 90 of the three dimensionalphotonic crystal.

As the method for forming the optical waveguide, for example, a methodcan be used in which one rod of the photonic crystal being in contactwith the defect portion 57 is removed.

Next, the step shown in FIG. 5I, is a sub-step of removing the sacrificelayers 56 for forming the three dimensional crystal structure, together.

As the process for removing the sacrifice layers 56, for example, achemical etching process using an appropriate liquid etchant or gaseousetchant is included.

After being subjected to the above steps, the main part of the visiblelaser device is produced.

EXAMPLES

Hereinafter, examples of the laser apparatus according to the presentinvention will be described with reference to the attached drawings.

Example 1

Now, using FIGS. 5A, 5B, 5C, 5D, 5E, 5F, 5G, 5H and 5I, Example 1 willbe described. In this example, the visible laser light device is a laserdevice of a current injection system using a heterostructure as anactive portion.

First, as illustrated in FIG. 5A, an alignment mark 52 is formed on aquartz substrate 51.

In forming the alignment mark 52, first, a resist pattern is formed onthe quartz substrate 51 by means of a photolithography process.

Chromium (Cr) in a thickness of 100 nm and gold (Au) in a thickness of500 nm are then vapor deposited on the quartz substrate 51 sequentially.

Then, the resist is dissolved using an organic solvent such as acetoneto form the alignment mark 52 in a predetermined number in predeterminedpositions by means of a lift-off process (the step not illustrated).

Next, as illustrated in FIG. 5B, by means of sputtering, a transparentmaterial thin film 53 made of titanium oxide (TiO₂) is formed on thesubstrate 51.

The thickness of the transparent material thin film 53 is about 90 nm.During sputtering, in order to protect the alignment mark 52, bycovering the surface of the substrate 51 with a metal mask, titaniumoxide is deposited only on a part of the substrate 51 on which a film isto be formed.

Moreover, for the sputtering, a TiO_(x) (x≈2) target is used, but theobtained thin film is amorphous TiO_(y) (y≈2)

Without heat-treating the amorphous titanium oxide film, a photoniccrystal is formed as such.

As needed, after the sputtering, by heat-treating the amorphous titaniumoxide thin film in an oxygen atmosphere under appropriate conditions, acrystalline titanium oxide thin film can be obtained.

As the optimum conditions of the heat treatment, the maximum temperatureis 500° C. to 900° C., more preferably 600° C. to 700° C., and theretention time at the maximum temperature is 10 minutes to 10 hours,more preferably about 30 minutes.

Next, as illustrated in FIG. 5C, using the alignment mark 52 as apositional reference, a mask pattern is formed on the titanium oxidethin film 53.

Here, first, a Cr thin film is formed in a thickness of about 50 nm onthe titanium oxide thin film 53, and then a resist is applied and apredetermined resist pattern 54 is formed by means of an electron beamexposure process.

Then, by means of an ion milling process, the resist pattern 54 istransferred onto the Cr thin film to form a secondary mask pattern 55.

The pattern is for forming a three dimensional woodpile photoniccrystal, and the period, the width and the length of the rods are about250 nm, about 90 nm, and about 100 μm, respectively.

Moreover, the number of the periods in plane of the woodpile rods isabout 400.

Next, as illustrated in FIG. 5D, using both of the resist pattern 54 andthe secondary mask pattern 55 as masks, the titanium oxide thin film 53is processed by means of reactive ion etching.

As the reaction gas for the reactive ion etching, a fluorine containinggas, for example, C₄F₈, SF₆, or a mixed gas of CHF₃ and CF₄ can be used.After that, using oxygen plasma, the resist pattern 54 is removed, andthe Cr pattern 55 is removed, by means of wet etching.

Next, as illustrated in FIG. 5E, first, on a thin film containing thefirst layer structure 71, a copper (Cu) thin film is deposited in athickness of about 500 nm as a sacrifice layer 56.

Then, by means of chemical mechanical polishing (CMP), the Cu thin film56 is flattened until the first layer structure 71 is exposed.

Next, as illustrated in FIG. 5F, using the alignment mark 52 as apositional reference, by repeating the sub-steps illustrated in FIGS.5B, 5C, 5D and 5E eight times, the first portion 70 of the threedimensional photonic crystal and the second portion 80 of the threedimensional photonic crystal are formed. Here, the second portion 80 ofthe three dimensional photonic crystal is only one layer, where a defectportion 57 for housing an active portion for generating light, and anoptical waveguide (not shown) are provided. The defect portion 57 andthe optical waveguide (not shown) can be formed by, for example,designing the shape of a mask pattern so as to cut off a half of one rodlocated approximately at the center when making the layers of the secondportion 80 of the photonic crystal.

Here, the main material of both of the first portion 70 and the secondportion 80 of the three dimensional photonic crystal is titanium oxide.

However, in the film formation for forming the first portion 70, byincorporating Nb or Ta into a high-purity TiO_(x) (x≈2) sputteringtarget, the titanium oxide thin film is provided with metal-likeconductivity.

On the contrary, in the film formation for forming the second portion80, using the high-purity TiO_(x) (x≈2) sputtering target as such, aninsulating titanium oxide thin film is formed.

Next, as illustrated in FIG. 5G, after the defect portion 57 is formed,an active portion 60 for generating light is formed in the defectportion 57.

The constitution of the active portion 60 is, for example, aheterostructure of GaN/TiO₂/GaN.

The formation thereof is performed by, for example, a method such asillustrated in FIGS. 6A, 6B, 6C and 6D.

First, as illustrated in FIG. 6A, as a first portion 61 of the activeportion, a GaN thin film structure is formed in the defect portion 57 bymeans of chemical vapor deposition induced by irradiation with anelectron beam.

The thickness and the size of the GaN thin film are set to about 30 nmand about 90 nm, respectively. After that, a focused Si-ion beam isselectively injected into the first portion 61.

Next, as illustrated in FIG. 6B, by means of chemical vapor depositioninduced by irradiation with an electron beam, a Ti thin film structureis formed on the first portion 61 of the active portion.

The thickness and the size of the Ti thin film are set to about 30 nmand about 90 nm, respectively.

After that, the Ti thin film is oxidized in an oxygen atmosphere bymeans of a partial heat treatment utilizing irradiation with an electronbeam or a laser, whereby a TiO₂ thin film is obtained as a secondportion 62 of the active layer. Next, as illustrated in FIG. 6C, on theTiO₂ thin film to be used as the second portion 62 of the active layer,a GaN thin film structure 63 is formed by means of chemical vapordeposition induced by irradiation with an electron beam. The thicknessand the size of the GaN thin film are set to about 30 nm and about 90nm, respectively. After that, a focused Mg-ion beam is selectivelyinjected into the first portion 61.

Finally, by means of a partial heat treatment by irradiation with anelectron beam or a laser, Si and Mg respectively injected into the firstportion 61 of the active portion and the third portion 63 of the activeportion are activated.

Then, an n-type GaN thin film and a p-type GaN thin film are formed inthe first portion 61 of the active portion and in the third portion 63of the active portion, respectively.

By performing the above-mentioned processes, in the defect portion 57 ofthe photonic crystal, an n-GaN/i-TiO₂/p-GaN heterostructure (wherein “i”means “insulating”) such as illustrated in FIG. 6D is obtained.

Then, as illustrated in FIG. 5, the third portion 90 of the threedimensional photonic crystal is formed.

First, the sub-step illustrated in FIG. 5E is performed.

Next, by repeating the sub-steps illustrated in FIGS. 5B, 5C, 5D and 5Eeight times, the third portion 90 of the three dimensional photoniccrystal is formed.

The structure of the third portion 90 of the three dimensional photoniccrystal is substantially the same as the structure of the second portion80 of the three dimensional photonic crystal.

Here, in the film formation for forming the third portion 90, byincorporating Nb or Ta in a high-purity TiO_(x) (x≈2) sputtering target,a titanium oxide thin film is provided with metal-like conductivity.

Moreover, here, the upper part of the active portion 60 is brought intoclose contact with the lower part of the third portion 90 of the threedimensional photonic crystal so as to be electrically connected to eachother.

Then, as illustrated in FIG. 5I, Cu that is the sacrifice layer 56 forforming a three dimensional crystal structure is dissolved using anappropriate liquid etchant to thereby be removed together.

By performing the above-mentioned steps, a visible light laser device isformed which uses the first portion 70, the second portion 80, and thethird portion 90 of the three dimensional photonic crystal as the lowerelectrode of the active portion 60, the insulating layer, and the upperelectrode of the active portion 60, respectively.

Example 2

In example 2, a production method of a laser apparatus of an opticalinjection system in which a visible light laser device is formed using aquantum dot as an active portion will be described.

Here, since the structure of the visible light laser light device andthe production steps thereof are similar to those described withreference to FIGS. 5A, 5B, 5C, 5D, 5E, 5F, 5G, 5H and 5I, the detailwill be omitted, and only significantly different parts will bedescribed.

First, the active portion 60 of the visible light laser device in thisexample is a GaN quantum dot.

The quantum dot is cylindrical, and the diameter thereof is 5 nm to 50nm, and the height is 10 nm to 90 nm. In this case, the upper part ofthe GaN quantum dot may be not in contact with the third portion 90 ofthe photonic crystal.

As the production method of the GaN quantum dot, an electron beaminduced chemical vapor deposition process is used.

In addition, since the first portion 70 and the third portion 90 of thethree dimensional photonic crystal of this example are not required tobe used as electrodes, the materials thereof may be composed of onlyinsulating titanium oxide.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2006-074942, filed Mar. 17, 2006 which is hereby incorporated byreference herein in its entirety.

1. A laser apparatus comprising a light-emitting region on a substrate,and a periodic refractive index structure comprising an i-type materialprovided at a periphery of the light-emitting region.
 2. The laserapparatus according to claim 1, wherein the i-type material is i-typetitanium oxide.
 3. The laser apparatus according to claim 1, wherein theperiodic refractive index structure is formed of a three dimensionalphotonic crystal.
 4. The laser apparatus according to claim 1, wherein alayer comprising the light-emitting region and the periodic refractiveindex structure has an electrode of a three dimensional photonic crystalcomprised of a p-type titanium oxide material on one side of an upperside and a lower side of the layer, and an electrode of a threedimensional photonic crystal comprised of an n-type titanium oxidematerial on the other side of the layer.
 5. A laser apparatus comprisinga light-emitting region between a first electrode and a second electrodeon a substrate, wherein at least one of the first and the secondelectrodes comprises a periodic refractive index structure.
 6. The laserapparatus according to claim 5, wherein both the first and the secondelectrodes comprises a periodic refractive index structure.
 7. The laserapparatus according to claim 6, wherein one of the first and the secondelectrodes which is located on the side from which laser light is outputby the laser has a transparency with respect to the output laser light.8. The laser apparatus according to claim 5, wherein a region whichsurrounds the light-emitting region between the first and the secondelectrodes is formed of an i-type three dimensional photonic crystal. 9.A method of producing a laser apparatus, comprising: forming a firstlayer comprising a three dimensional periodic refractive indexstructure; forming a second layer with a periodic structure region onthe first layer; forming a recess in the second layer and forming anactive portion for generating light in the recess; and forming a thirdlayer comprising a three dimensional periodic refractive index structureon the second layer containing the active portion.
 10. The productionmethod according to claim 9, wherein the second layer is formed of ani-type material.
 11. The production method according to claim 9, furthercomprising providing a waveguide for extracting light outside, in thethree dimensional periodic refractive index structure of at least one ofthe first and the third layers.
 12. The production method according toclaim 9, wherein the three dimensional periodic refractive indexstructure of at least one of the first and the third layers is formed ofa material which is transparent with respect to visible light.
 13. Theproduction method according to claim 12, wherein the material which istransparent to visible light comprises any one of titanium oxide (TiO₂),gallium nitride (GaN), zinc oxide (ZnO), and indium tin oxide (ITO) as amain component.
 14. The production method according to claim 9, whereinthe active portion comprises a material which generates visible laserlight.